chamber pressure?

eon_shift · April 21, 2007, 03:11 PM

How do you measure it and what is dangerous i hear people talking about it but dont know how they would be able to tell.

brickeyee · April 21, 2007, 03:16 PM

You measure it using either a lead or copper crusher or the more modern piezo sensor.
The lead and copper crusher method only measures peak pressure, with some losses for the mass of the moving portions of the system and other more systemic errors.
The piezo method and a storage oscilloscope will provide a complete curve showing the pressure as a function of time. It is far more sensitive and precise.

What is dangerous depends on the cartridge type and the gun it will be fired in.
Modern bolt action rifles can run well up into the 65,000 PSI range, while older guns are often limited to 15,000 to 25,000 PSI due to metallurgy and design.

eon_shift · April 21, 2007, 07:44 PM

is checking pressure absolutely needed

williamd · April 21, 2007, 09:04 PM

Not if you stay within the guidelines of the reloading manuals and your weapon is in decent shape.

eon_shift · April 21, 2007, 10:30 PM

so theres no real need for me to get one unless i want to make up some crazy load?

jamaica · April 21, 2007, 10:37 PM

You don't need to actually measure the pressure to know when it is too high. There are several indications of high pressure.

Excessive recoil, the bolt may have to be hammered open, the primer will be excessively flattened, there may be a ridge around the firing pin dent, and brass may have been extruded into the extractor slot. The case head may show some enlargement when measured with a micrometer.

Castaway · April 22, 2007, 05:30 AM

Case head measurement is not a reliable means to determine excessive pressure. Handloader magazine has had extensive articles about it. In straight walled pistol cases, difficult extraction is not always a good sign because of the time you get to that point, sometimes you can be twice the pressure limit. Flattened and cratered primers are fairy reliable. The only way to find out how much pressure is developed is a strain gauge of some sort. There's a company whose name occasionally surfaces that will test your ammo for a fee. Unless you have a good supply of uncommitted money I don't think you'd want to invest in the equipment.

brickeyee · April 22, 2007, 08:03 AM

You do not need to measure pressure.
Follow a good loading manual.
They rarely have loads that are excessive, but to make sure use more than one.
Many of the powder makers manuals are free, and combined with a larger manual (Lee, RCBS, Hornady, etc) you should be able to verify that listed loads are realistic.

Strain gauge systems are still relative and depend critically on steel properties and carefully calibrated test ammunition with known properties.
Piezo systems also require calibration but are far less dependent on parameters outside the sensor.

Jim Watson · April 22, 2007, 08:34 AM

YOU don't measure chamber pressure at all, unless you are a very serious amateur ballistician. It takes a good deal of equipment, preparation, and operation. As said, go by the book(s), the powder and bullet companies have the equipment and the specialists to be sure that the loads they publish are to industry standards.

Eyeball guesstimation of chamber pressures are not very reliable. One of the old time manuals, back when handloaders were considered to be competent adults, said to increase loads until ONE of several indicators of high pressure was seen, and then to reduce that load by 6%. But that amount of reduction was too much for the hotrodders, who would back off half a grain to just barely avoid glaringly obvious signs of excess pressre, even though it was still there; so the literature quit describing the procedure.

April 21, 2007, 03:11 PM	#1
eon_shift Member Join Date: April 16, 2007 Location: Canada Posts: 22	chamber pressure? How do you measure it and what is dangerous i hear people talking about it but dont know how they would be able to tell.

April 21, 2007, 09:04 PM	#4
williamd Senior Member Join Date: March 13, 2007 Location: SoCal Posts: 801	Not if you stay within the guidelines of the reloading manuals and your weapon is in decent shape. __________________ "Outlaw guns and only outlaws will have guns!" Unfortunately, we may be moving in that direction. NRA Benefactor, Conservative!, VN '64-'65. Never sell a gun or a car ... and retire rich!

April 21, 2007, 03:16 PM	#2
brickeyee Senior Member Join Date: December 29, 2004 Posts: 3,351	You measure it using either a lead or copper crusher or the more modern piezo sensor. The lead and copper crusher method only measures peak pressure, with some losses for the mass of the moving portions of the system and other more systemic errors. The piezo method and a storage oscilloscope will provide a complete curve showing the pressure as a function of time. It is far more sensitive and precise. What is dangerous depends on the cartridge type and the gun it will be fired in. Modern bolt action rifles can run well up into the 65,000 PSI range, while older guns are often limited to 15,000 to 25,000 PSI due to metallurgy and design.

April 21, 2007, 07:44 PM	#3
eon_shift Member Join Date: April 16, 2007 Location: Canada Posts: 22	is checking pressure absolutely needed

April 21, 2007, 10:30 PM	#5
eon_shift Member Join Date: April 16, 2007 Location: Canada Posts: 22	so theres no real need for me to get one unless i want to make up some crazy load?

April 21, 2007, 10:37 PM	#6
jamaica Senior Member Join Date: March 24, 2006 Location: Northern Utah Posts: 705	You don't need to actually measure the pressure to know when it is too high. There are several indications of high pressure. Excessive recoil, the bolt may have to be hammered open, the primer will be excessively flattened, there may be a ridge around the firing pin dent, and brass may have been extruded into the extractor slot. The case head may show some enlargement when measured with a micrometer.

April 22, 2007, 05:30 AM	#7
Castaway Member Join Date: February 2, 2007 Location: Dade City, FL Posts: 90	Case head measurement is not a reliable means to determine excessive pressure. Handloader magazine has had extensive articles about it. In straight walled pistol cases, difficult extraction is not always a good sign because of the time you get to that point, sometimes you can be twice the pressure limit. Flattened and cratered primers are fairy reliable. The only way to find out how much pressure is developed is a strain gauge of some sort. There's a company whose name occasionally surfaces that will test your ammo for a fee. Unless you have a good supply of uncommitted money I don't think you'd want to invest in the equipment.

April 22, 2007, 08:03 AM	#8
brickeyee Senior Member Join Date: December 29, 2004 Posts: 3,351	You do not need to measure pressure. Follow a good loading manual. They rarely have loads that are excessive, but to make sure use more than one. Many of the powder makers manuals are free, and combined with a larger manual (Lee, RCBS, Hornady, etc) you should be able to verify that listed loads are realistic. Strain gauge systems are still relative and depend critically on steel properties and carefully calibrated test ammunition with known properties. Piezo systems also require calibration but are far less dependent on parameters outside the sensor.

April 22, 2007, 08:34 AM	#9
Jim Watson Senior Member Join Date: October 25, 2001 Location: Alabama Posts: 18,543	YOU don't measure chamber pressure at all, unless you are a very serious amateur ballistician. It takes a good deal of equipment, preparation, and operation. As said, go by the book(s), the powder and bullet companies have the equipment and the specialists to be sure that the loads they publish are to industry standards. Eyeball guesstimation of chamber pressures are not very reliable. One of the old time manuals, back when handloaders were considered to be competent adults, said to increase loads until ONE of several indicators of high pressure was seen, and then to reduce that load by 6%. But that amount of reduction was too much for the hotrodders, who would back off half a grain to just barely avoid glaringly obvious signs of excess pressre, even though it was still there; so the literature quit describing the procedure.